Viscosity control in heavy media separation



J. J. BEAN VISCOSITY CONTROL IN HEAVY MEDIA SEPARATION Filed Dec. 27.1948 FFE@ April 7, 1953 C m l y n r x N m M M wr W m W. E i z www WF M ma a i M yr M N d. f o r 7. 7 WMP. N www N 4 MP a m 7 m 3. n, 460 Wi M .7y F .d

M @m P w N M M Mu n 7 n 7 M Mr. w .w w we m. 4 m M R a a a 4 PatentedApr. 7, 1953 VISCOSITY CONTROL IN HEAVY MEDIA SEPARATION James JosephBean, Riverside, Conn., assignor to American Cyanamid Company, New York,N. Y.,

a corporation of Maine l Application December 27, 1948, Serial No.67,440

1 Claim. (Cl. 209-39) This invention relates to an improvement in heavymedia separation of solid particles making use ofmagnetically-susceptible medium solids. In particular, the invention isconcerned with an improved method of controlling the viscosity of theseparatory fluid and the rate of settling of the medium solidstherethrough.

In the past few years, a growing industrial interest has developed invarious operations for the separation of solid particles by means ofgravity differentials. Therein a mixture of Darticles having diiferentspecific gravities is immersed in a fluid having a densityapproximating, and usually between the gravities of the particles to beseparated. In the more usual case Where the nuid density is intermediatethe specific gravities of the solids, the particles are separated into afloat fraction of lesser gravity than the fluid and a sink fraction -ofgreater gravity than the fluid. In operations where the uid is of lesserdensity than the lower gravity particles, a series of portions areobtained, each comprising a mixture of low-gravity particles in a sizeband having a selected settling rate and smaller but greater-gravityparticles having substantially the same settlingrate. The effect of theheavy density fluid is to spread the difference in size band between theparticles of differing gravity. Each portion then may be readilyseparated into low and high gravity fractions by simple screening.Variations have also been proposed in which centrifugal force is used toobtain a separating force greater than normal gravity.

In any case, auid of apparent density greater than unity is ordinarilyrequired. Industrially, the most useful of such fluids are suspensionsin water of medium solids which are so nelydivided as to besemi-permanently suspended. Further, since economically feasibleoperation reuuires recovery and reuse of the medium solids, the moredesirable of such separatory fluids are those in which the medium solidsare magnetically-susceptible and 'have magnetic remanence so that theymay be magnetically recovered and/ for cleaned. Before reuse, the solidsare demagnetiZed. The presentinvention is particularly concerned withthose operations which make use `of such magnetic recovery and/orcleaning.

Certain problems are involved in making up and maintaining anysatisfactory heavy-media separatory fluid. Among other problems, forexample, depending upon the size and density of the medium solids, adensity gradient sets up in the separatory vessel, due, not only tosettling of the heavy gravity particles but also of the mediurn solids.This must be controlled within certain limitations. Otherwise, operationbecomes inemcienu if not actually impractical.'

Another diiculty is occasioned by the amount of medium solids Which mustbe suspended, In

2 order to achieve the desired apparent density, the requisite amount ofsolids which must be suspended may produce a fluid of too greatviscosity to permit eflicient and rapid settling therethrough of thesolids mixture being treated. Especially is this true when the amountsof fines in the mixture to be treated are large. They not only settleslowly but aggravate the diinculty. Viscosity, therefore, must becontrolled within certain limits. Another problem lies in the fact thatrecirculation of the medium solids requires a certain differential headbetween the densier and separatory vessel circuit. As this becomesexcessive, operation also becomes ineflicient.

In the past, various proposals have been made to control these factorsand overcome at least in part the difficulties which they produce. Not

-all ofthese procedures, however, have been wholly satisfactory. Someare not operable to the desired efficiency. Some require excessiveamounts of extra equipment. Some require so great a degree ,of controlthat operation cannot be equalized.

Itis, therefore, the principal object of the present invention to devisea procedure whereby in the use, recovery, and reuse ofmagnetically-susceptible medium solids the viscosity of the separatoryuid, the degree of iiocculation of medium solids, the rate of settlingof'medium solids and the kindred problems and the like may be accuratelyand easily controlled and the head requirements between the densier andseparatory vessel medium circuits may be reduced.

Surprisingly, the desired objects of the present .Y

invention are readily accomplished by recognition of a fact previouslynot recognized about magnetic recovery systems. It is now generallyrecognized that the medium solids, before reuse, must be demagnetized inorder to prevent flocculation and 4obtain uniform dissemination. The

general practice, therefore, has been to demag- Anetize all mediumsolids which are recovered and cleaned for reuse. 4

In accordance with the present invention, it

has been found that there is no necessity for demagnetizing all thecleaned medium solids. In other words, the process of the presentinvention is based on the new principle that the amount of medium whichis demagnetized, within reasonable limits, may be entirely independentof the amount of medium which is cleaned. By separating these twofunctions the degree of demagnetization of the total amount of solids incirculation may be accurately controlled. By controlling this factor,the degree of flocculation of the medium solids also can be controlledand as l a result control is obtained of the density differential in thefluid in the separatory vessel.

Once. the principle of the present invention is lrecognized, it isapparent that it is not necessarily dependent upon any one particulararrangement f apparatus. Therefore, the invention will be more fullydiscussed in conjunction with the accompanying drawing which exhibitsschematically, in Figures 1, 2 and 3, several useful arrangements ofapparatus and. Ythe'iiowof,iiuids therethrough. These gures arediagrammatic and for illustrative purposes only. Therefore, onlytreatment of the sink fraction is shown, treatment of the oat fractionbeing lomitted for purposes of clarity. The treatment thereof is similarand discussed below.

In a typical arrangement, such as is schematically diagramed in Figure1, there is shown a conventional separatory vessel l having an externallift conduit 2 for the heavy gravity fraction. The external lift conduitis surrounded for part of its length by a demagnetizing coil'3 throughthe conventional leads of which varying'amcunts of alternating currentmay be applied. The sink fraction is dis-chargedonto a suitable drainagescreen i which has a suitable receiver :5 for the drainage medium which`passes therethrough. The drained fraction passes vto a conventionalwashing screen S. From the'latter, the Washings are collected in asuitable receiver 1 and passed to a conventional medium recovery andcleaning circuit generally indicated at 8. As shown, a portion of thedrainage medium may also be sent to the cleaning system 8. The remainderof the drainage medium is combined with cleaned, densified, butotherwise not demagnetized, medium from the medium cleaning circuit 8.This is returned as by a suitable pump 9 to `the separatory vessel l.Asnoted above, for purposes of illustration only the sink fractiontreatment is shown. A similar setoi" screens-is of course `provided forthe lighter-gravity fraction, the screen under flows being-eitherseparatelytreated or combined with those from screens 4 and 6. Thescreening, washing and recovery systems, except as to the location ofthe demagnetizing coil andthe extent of demagnetization, areconventional.

In Figure 2 a somewhat diierent liiow using the same apparatus isindicated. Instead of oombining the cleaned, densiied but notdemagnetized medium in combination with the sink screen-drainage medium,it is returned vdirectly to separatory vessel I However, a supplementaldemagnetizing coil is is provided in this line, which by Varying thecurrent therethrough may be made tor further `control the extent oftotal demagnetization. If desired, as shown, a portion thereof may beused to prewet a portion of the feed. In many cases where `coil l0 is.used sufcient control can kbe obtained by its use alone and coil 3 maybe powered but 'lightly' or even discarded.

In Figure, 3. a somewhat diierentz arrangement is shown. The separatoryvessel I, instead of being equipped with the. external lift 2, isprovided with an internal liftl Il'. The screen arrangement i's similarto that in Figure 2 as is the return of the cleaned, densied medium, acoil it! being provided in the line from the cleaning and densifymgsystem 8. Demagnetizing coil 3, however, instead ofbeinglocated on theSink lift, is around the conduit through which the drainage medium isrecycled. in many cases this is physically a simpler system to installandthe degree of control obtained will be similar to that of thearrangements, shown inFiigures lY and 2,. lf so desired however, coil '3instead of being located as in Figure 3 couldY have been placed aboutthe sink lift conduit l l. It might be placed either above the fluid intank l or submerged therein.

Ato be demagnetized may be laid down.

4 `From theioregoingzitjs;believedthat it will be clear that the presentinvention-involves certain elements of operating practice but thatotherwise it may be adapted to substantially any heavy' ,mediaseparation Aprocedure using magnetically' recoverable medium solids.These elements are the separation of the extent to which medium isdemagnetized from the amount of medium cleaned and the provision forcontrol of the extent of the totaldemagnetizing action.

,Thiszlatter may be obtained, either by varying the amount ofdemagnetizing energy applied to a substantially constant fluid nowthrough the demagnetizing eld, or b-y varying the amount of materialpassed through either'a constant or a controlled but variabledemagnetizing field. The former is shown in Figures land 2, the latterin Figures 2 Yand 3. In either event, an accurate control is obtained ofthe extent of demagnetizo- .tion of the total amount of magnetiaablesolids be a major portion. Only ya 'relatively email amount Yci residualmagnetism in the solids in the separatory vesselis ordinarily'requiredto obtain the control accompiished by the present invention. The preciselimits must be selected and governed by the 'size of the apparatus andthe nature of the material Vin use. Obviously the residual magneticinfluence used as viscosity control shouid not be too Vgreat asotherwise excessive occulation of the medium will occur, the densitygradient then will become excessive and the operation will .lose itsutility.

claim:

In the separation of mixtures of solid particles `of differing specificgravities by heavy-media separation accomplished Vin a fluid comprisinga suspension in a liquid of .nely-divded magnetizable medium solidswherein a portion of the medium solids removed with the separatedproducts is drained therefrom and returned to the separatory operationand the remainder is magnetically recovered and cleaned for reuse; theimproved method of controlling the viscosity, degree of iloeculation anddensity differential in the .separatoryJ fluid which comprises:controlling the degree of demagnetization of the'total amount ofmediurnl solids in rcirculation by varying the amount .of ow of recycledmedium solids and the Ypower `input to a demagnetizing `held.

JAMES JOSEPH BEAN.

REFERENCES CITED The following references are of record in the file oithis patent:

UNITED STATES PATENTS Number Name Date 2,373,635 Wuensch Apr. 10,FOREIGN PATENTS Number Country' Date 828,613: France Feb. 21, 1933679,429 Germany Aug. 5, 1939

